The Kilroot mine near Carrickfergus, Co. Antrim, which is owned by the Irish Salt Mining and Exploration company (ISME), has been in operation since 1965.

The only rock salt mine on the island of Ireland, it currently produces half a million tons of de-icing rock salt each year.

The salt is used locally, in the Republic and in the UK, and until as recently as 2008 the U.S. was also a customer, with Irish salt sprinkled on roads throughout the northeast.

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The majority of salt used in the U.S. now comes from Chile, but a representative from the ISME told IrishCentral it is possible that they could someday resume exporting to America, depending on demand.

Unlike table salt, which comes from the sea, rock salt is coarse and gritty in texture. Both forms start as sodium chloride, but rock salt is typically treated with strong anti-caking agents for ease of transportation and use. It works as a de-icing mechanism because of its low freezing point, which causes snow and ice to melt and prevents it from re-freezing. Irish salt is noted for its brownish hue.

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The Kilroot mine is a large underground salt deposit that formed millions of years ago during the Triassic period, when the land that is now the island of Ireland was covered by seawater. When the water evaporated, it left behind a large salt deposit, which in time was covered by land.

A 2km network of conveyors connects the heart of the salt mine with the surface. The salt is produced by a process known as room and pillar dry mining, one of the oldest mining methods. The salt bed is undercut, drilled and blasted, and a Webster rotary drill then carries out a process called roof scaling.

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The broken salt is transported to the crushing plant – also underground – and then brought to the surface, where it is packed into trucks. Shipping containers are also loaded with salt on the north shore of Belfast Lough and sent on their way.

The massive snow storm that blanketed Ireland and the UK in the winter of 2009 and 2010 (the Big Freeze) brought to light concerns about the mine’s supply running low, with forecasts that it would be depleted by 2012.

In March 2010, ISME received permission from the Northern Ireland Planning Service to expand the mine by 279 hectares – the equivalent of 340 international soccer fields – guaranteeing its survival for at least 30 more years.